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Enhanced drinking water supply through harvested rainwater treatment

Vincenzo Naddeo, Davide Scannapieco ⇑ , Vincenzo BelgiornoSanitary Environmental Engineering Division – SEED, Dept. of Civil Engineering, University of Salerno, Via Ponte don Melillo, 84084 Fisciano, SA, Italy

a r t i c l e i n f o

Article history:Received 14 December 2012Received in revised form 3 June 2013Accepted 8 June 2013Available online 17 June 2013This manuscript was handled by LaurentCharlet, Editor-in-Chief, with the assistanceof P.J. Depetris, Associate Editor

Keywords:Developing countriesDrinking water treatmentHousehold water supplyRainwaterSmall communitiesWater management

s u m m a r y

Decentralized drinking water systems represent an important element in the process of achieving theMillennium Development Goals, as centralized systems are often inefcient or nonexistent in developing

countries. In those countries, most water quality related problems are due to hygiene factors and patho-gens. A potential solution might include decentralized systems, which might rely on thermal and/or UVdisinfection methods as well as physical and chemical treatments to provide drinking water from rain-water. For application in developing countries, decentralized systems major constraints include low cost,ease of use, environmental sustainability, reduced maintenance and independence from energy sources.This work focuses on an innovative decentralized system that can be used to collect and treat rainwaterfor potable use (drinking and cooking purposes) of a single household, or a small community. The exper-imented treatment system combines in one compact unit a Filtration process with an adsorption step onGAC and a UV disinfection phase in an innovative design (FAD – Filtration Adsorption Disinfection). Alltests have been carried out using a full scale FAD treatment unit. The efciency of FAD technology hasbeen discussed in terms of pH, turbidity, COD, TOC, DOC, Escherichia coli and Total coliforms . FAD technol-ogy is attractive since it provides a total barrier for pathogens and organic contaminants, and reduces tur-bidity, thus increasing the overall quality of the water. The FAD unit costs are low, especially if comparedto other water treatment technologies and could become a viable option for developing countries.

2013 Elsevier B.V. All rights reserved.

1. Introduction

Decentralized approaches to water supply issues have been al-ready successfully applied in many parts of developing and transi-tion countries. These decentralized solutions deal with bothquality and availability problems and include the direct use of alternative water sources (groundwater, rivers or rainwater),household-based water treatment units, dual tap water systemsand distribution and sale of ready-to-use treated water ( Gadgil,1998; Mintz et al., 2001; Belgiorno and Napoli, 2000 ).

As water shortages occur more often, the search for alternative

water sources and ways to promote its rational use is relevant notonly to water-stressed regions but also to secure a stable watersupply that allows for rising water demand, rapid urbanizationand climate change ( Ghisi et al., 2006; Villareal and Dixon, 2005;Mun and Han, 2012; Belgiorno et al., 2013; Naddeo et al., 2013 ).

In some semi-arid areas of the world, rainwater harvesting hasbeen promoted for a long time as a useful technology, able to pro-vide local settlements with water. For example, in 50% of the Tan-zania area, people completely rely on rainwater for their survival(Mbilinyi et al., 2005 ).

The efciency and feasibility of rainwater-based supply systemshave been studied by many authors ( Eroksuz and Rahman, 2010;Ghisi et al., 2007; Ghisi and Ferreira, 2007; Jones and Hunt,2010; Khastagir and Jayasuriya, 2010; Li et al., 2010; Rahmanet al., 2012 ). Domènech and Saurí (2011) argue that for this kindof treatment units the economic feasibility can be determinedthrough a detailed analysis of the end-user needs, usually re-stricted to a few options. In addition, in water stressed areas theeconomic feasibility threshold value tends to be lower.

Rainwater harvesting and treatment provides water directly tohouseholds allowing family members to have full control of their

own water system, which greatly reduces centralized operationand maintenance costs. There are also examples of rainwater har-vesting systems developed for entire settlements, in which water iswithdrawn from roads or elds ( Gould and Nissen-Petersen, 1999 ).The main disadvantages of rainwater harvesting are the depen-dence on rainfall seasonal variability, the uncertainty of precipita-tions and also the rainwater quality, which is characterized by auctuating behaviour; in addition, diseases may spread over acommunity since rainwater has to be stored, sometimes for a longperiod. Several techniques used to collect precipitation runoff overroads, elds or roofs after dry periods may provide nal users withcontaminated water supply due to deposited pollutants that areushed away during precipitation ( Zhu et al., 2004 ).

0022-1694/$ - see front matter 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.jhydrol.2013.06.012

⇑ Corresponding author. Tel.: +39 089969337; fax: +39 089969620.E-mail address: dscannapieco@unisa.it (D. Scannapieco).

Journal of Hydrology 498 (2013) 287–291

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Several technologies have already been explored or used, aloneor in combination, as end-of-pipe systems to treat the fraction of rainwater that is to be used for drinking purposes ( Sobsey, 2002 ).Some of these methods, such as boiling water, are traditionallyand widely used, although they may not always be the optimalsolution ( Mintz et al., 2001 ) in terms of nancial issues as wellas nal water quality.

Solar water disinfection (SODIS) is a basic technology used toimprove the microbiological quality of drinking water by usingsolar radiation as to destroy pathogens ( Mintz et al., 2001 ). Apotential limitation of SODIS, besides its dependence on sunlightfor disinfection, is that the treatment process is rather complex.

UV irradiation with lamps has raised renewed interest in re-cent years because of its well-documented ability to extensively(>99.9%) inactivate two waterborne, chlorine-resistant protozo-ans, Cryptosporidium parvum oocysts and Giardia lamblia cysts, atrelatively low irradiation doses. However, UV lamp disinfectionhas some disadvantages when used as a drinking water disinfec-tant at household level. Organic matter, turbidity and certain dis-solved contaminants can interfere with or reduce the efciency of microbial inactivation. These lamps require periodic cleaning,especially if placed in a submerged conguration; moreover, theyhave a nite lifespan and must be periodically replaced ( Gadgil,1998 ).

Chemical treatment is widely used for disinfection purposes atfull scale facilities. Of the drinking water disinfectants, free chlo-rine is the simplest, most widely used and the most affordableone. It is highly effective against nearly all water-borne pathogens,with the notable exception of C. parvum oocysts and the Mycobac-teria species (Sobsey, 2002; Mintz et al., 2001 ). However, the socio-cultural acceptance of disinfection with chlorine-containing re-agents is low in some cases, due to taste and odour impact prob-lems ( Murcott, 2005 ); in addition, chlorine gas storage posessignicant health risks and is therefore used only at large waterfacilities

Slow sand ltration has been adapted for household use and isalso known as Biosand ltration (BSF). Biosand lters are tankslled with sand in which a bioactive layer is allowed to grow asa means of eliminating disease-causing microorganisms. Severalstudies show that BSF removes bacteria consistently, if not com-pletely, on average in the range 81–100%, and protozoa by99.98–100%. However, these lters have limited viruses removalefciency ( Lantagne et al., 2007; Naddeo and Belgiorno, 2007 ).

Furthermore, paper, ber or fabric lters may be applied athousehold level. They can be effective in the removal of largerwater-borne pathogens such as free-swimming larval forms ( cerca-riae ) of schistosomes and Faciola species , guinea worm larvae withintheir intermediate crustacean host ( Cyclops), and bacterial patho-gens associated with relatively large copepods and other zooplank-ton in water, such as the bacterium Vibrio cholerae (Sobsey, 2002 ).

However, these lters are not recommended for the treatment of household water supply because their pores are too large to signif-icantly retain viruses, bacteria and smaller protozoan parasites(Sobsey et al., 2008 ).

Activated carbon lters, often in the form of pressed blocks, fol-lowed by UV disinfection or pre-coated with silver (Ag), are used astable-top units for additional tap water treatment ( Abbaszadeganet al., 1997 ). However, they have a only limited operating life (6–8 months) and relatively high costs.

This work focuses on an innovative decentralized system to col-lect and treat rainwater for potable use (drinking and cooking) of asingle household or a small community. The tested unit is com-posed of a Filtration phase, followed by Adsorption on GranularActivated Carbon (GAC) and UV Disinfection, in an innovative de-

sign (FAD – Filtration Adsorption Disinfection).

2. Materials and methods

2.1. FAD treatment unit

The FAD system has been reported in Fig. 1. All tests have beencarried out using a full scale FAD treatment unit at xed ow rate(30 L/h) on harvested rainwater for a total treatment time of 25 h.

The unit is composed of two separate elements, and it can workboth with and without pumping. The pre-ltration unit is providedwith a membrane, characterized by a porosity of 75 l m. The FADunit combines adsorption on GAC, microltration at 0.5 l m andUV disinfection. The microltration step is located immediatelyafter GAC treatment and there the feed is exposed to UV light irra-diation ( Fig. 1), therefore this zone is hereafter referred as hybridFAD zone. UV light is produced by a 15 W low pressure lamp madeof hard quartz glass.

The rain has been harvested from the rooftop of a small buildinglocated in theexperimental wastewater treatmentstation at theUni-versity of Salerno (Italy) in a conventional water tank of 2500 L, dur-ing the period ranging from December 2008 to May 2009. The waterwas then treated on site with the FAD unit. The collected rainwaterwas stored in the tank for no more than 19 consecutive days.

Tests have been carried out with and without UV light. In orderto compare efciencies, another set of experiments has been com-pleted, using only the GAC adsorption step. The latter experimentalsetup has been characterized by identical operating conditions of the FAD unit in terms of GAC volume and available surface foradsorption; it has been housed into the twin reactor, in which boththe membrane and the UV lamp were removed.

2.2. Analytical methods

Analytical measurements were made at the EnvironmentalEngineering Laboratory of the University of Salerno, Fisciano (SA),Italy. The USEPA Standard Methods have been successfully used

for microbiological analyses. Acetate cellulose lters (0.45 l m poresize, Millipore, USA) were employed for sample ltration while m-endo medium (Oxoid, Italy) and Tryptone Bile X -Glucuronide (TBX)medium (Oxoid, Italy) were used respectively for Total coliformand Escherichia coli retention.

The results were expressed in terms of Colony Forming Unitsper 100 mL (CFU/100 mL). Absorbance measurements were per-formed using a k 12 UV–Vis spectrophotometer (Perkin Elmer,USA). Turbidity was detected using a turbidimeter (Model2100 N, Hach Lange AG, Germany). Total Organic Carbon (TOC)was determined using a Shimadzu TOC-5000A analyzer. ChemicalOxygen Demand (COD) and Total Suspended Solids (TSS) weremeasured following the AWWA–APHA–WEF Standard Methods(AWWA–APHA–WEF, 1998 ). The measurement of pH, conductivityand redox potential were carried out using a multiparametricprobe (Hanna Instruments, USA).

3. Results and discussion

3.1. Rainwater characterization

During the harvesting period, rainwater quality has been con-stantly monitored, and results showed a fair stability in terms of chemical-physical parameters, as reported in Table 1 and accord-ingly plotted in Fig. 3. High turbidity and a consistent concentra-tion of organic matter have been found; this is in accord withother previously published studies ( Gould and Nissen-Petersen,1999; Zhu et al., 2004 ). Finally, pH ranged from 5.5 to 7.1, with

an average value of 6.3.

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Water quality has also been monitored in terms of Total coli-form and E. coli, which signicantly scattered over time ( Fig. 2).This behaviour can be imputable to the presence of bacteria over

the rooftop; their concentration was considerably higher whenprecipitation occurred after several dry days.

3.2. Turbidity and bacteria removal

Turbidity is often used to represent the presence of particles inwater, which is a major parameter of water quality in drinkingwater treatment. During the experiments, the turbidity in theraw water was 25.88 ± 3.62 NTU, on average. A moderate removalefciency of 22.7 ± 8.7% was achieved by the pre-ltration unit, sothat 20.33 ± 2.16 Nephelometric Turbidity Units (NTU) level stillremained in the efuent. However, the FAD unit has proven itself to be able to reduce turbidity as much as to 0.42 ± 0.06 NTU, thatcan be attributed to both the GAC adsorption and microltration

steps. Approximately 99.9% of the feed suspended solids has beenremoved in the process.

Coliforms are often employed as the microbiological parameterfor the pathogenic safety of treated water. In the FAD efuent,the concentration of Total coliforms was equal to 0 ± 0 CFU/100 mL, while in raw rainwater the same concentration attainedthe value of 328 ± 126 CFU/100 mL ( Fig. 2). The pre-ltration unitmembrane nominal pore size was bigger than the average diame-ter of coliforms , therefore the complete removal of Total coliforms inthe FAD process might be attributed to both the separation effect of the GAC lter and disinfection-oxidation effect of the UV lamp. Dis-infection efciency was determined through E. coli monitoring aswell. A total removal of E. coli by the FAD process is also reportedin Table 1 , which can be compared with the 151 ± 32 CFU/100 mL value in raw water ( Fig. 2).

3.3. Organic matter removal

Organic matter can be divided into a Particulate Organic Matter(POM) and Dissolved Organic Matter (DOM) fraction. POM could beeasily removed even through conventional water treatment pro-cesses. On the other hand, DOM is one of the most critical concerns

in drinking water treatment, since this fraction is potentially haz-ardous and difcult to be eliminated ( Sobsey, 2002 ).

The performance of the FAD process in terms of DOM removalas DOC and UV 254 was investigated and illustrated in Fig. 3. Itcan be seen that Dissolved Organic Carbon (DOC) in the raw waterwas reduced by 26.3 ± 6.0% in the FAD unit without any UV lamp;on the other hand, the total removal efciency increased to37.3 ± 5.9% thanks to the UV irradiation and the subsequent oxida-tion effect. As for UV 254 , the recorded removal efciency is equal to29.9 ± 4.7% and 38.3 ± 6.7% after the treatment, without and withUV irradiation, respectively. Thus, it can be concluded that theinuent DOM is mainly removed through GAC adsorption.

The contribution of UV irradiation over the Natural OrganicMatter (NOM) removal can be attributed to oxidative effects on

dissolved organic matter and to the disinfection process that takesplace in the reactor. On the one hand, although the raw rainwater

Fig. 1. Experimental setup of the FAD unit (left) and its section.

Table 1

Comparison of pollutants removal by the FAD process and the separate conventional GAC adsorption unit.

Analytical parameters Raw water FAD process Separate GAC

Efuent Removal (%) Efuent Removal (%)

Turbidity (NTU) 25.88 ± 3.62 0.42 ± 0.06 98.3 ± 1.6 2.13 ± 0.42 59.7 ± 12.7COD (mg/L) 4.79 ± 0.56 2.39 ± 0.35 49.9 ± 7.5 3.70 ± 0.63 22.8 ± 8.7TOC (mg/L) 5.952 ± 0.71 3.383 ± 0.43 42.8 ± 6.9 4.278 ± 0.49 27.8 ± 7.1DOC (mg/L) 5.398 ± 0.517 3.383 ± 0.436 37.3 ± 5.9 3.169 ± 0.419 29.3 ± 6.0UV254 (cm 1) 0.086 ± 0.008 0.052 ± 0.003 38.3 ± 6.7 0.060 ± 0.005 29.9 ± 4.7Escherichia coli (CFU/100 mL) 328 ± 126 0 ± 0 99.99 ± 0.0 108 ± 92 67.9 ± 14.3Total coliforms (CFU/100 mL) 152 ± 32 0 ± 1 99.99 ± 0.0 61 ± 29 59.8 ± 19.1

Fig. 2. Bacteriological raw rainwater characterization in terms of Total coliformsand Escherichia coli (respectively, from the lower to higher value in terms of detected colonies: min, 25 percentile, average, 75 percentile, max).

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had already gone through the pre-ltration step, there still was aremaining fraction of DOM. On the other, the GAC adsorption sur-face and microltration layer in the FAD reactor can provide anexcellent surface for the attachment of microbial communities(Guo et al., 2008 ), thus enhancing the DOM removal through bio-degradation of the adsorbed DOM by the microorganisms on GAC

surface. Consequently, the UV irradiation still contributed to10.0% of the DOC and 8.4% of the UV 254 removal even after GAC mi-cro-ltration, as discussed above.

COD and TOC are widely used in water treatment as surrogateparameters to represent the content of organic matter. As illus-trated in Fig. 3, COD and TOC were removed by 22.8 ± 8.7% and27.8 ± 7.1% as well as 49.9 ± 7.5% and 42.8 ± 6.9% after the treat-ment without and with UV irradiation, respectively. There was stillPOM in the GAC efuent with an average concentration of 0.309 mg/L as TOC, which was probably due to the presence of bio-lm residues developed over the GAC surface. However, the POMconcentration can be easily reduced by the micro-ltration-layerand UV oxidation if placed in the same unit.

A synergetic effect has been observed among the GAC, microl-tration and UV irradiation in the FAD process referring to the dis-solved and total organic matter removal simultaneously, i.e. theGAC was able to remove a large amount of DOM in water, thedownstream microltration further eliminated the POM and nallyUV irradiation provided a complete disinfection with a stable foul-ing formation on the quartz glass, which is dependent on the or-ganic matter concentration of the feed ( Liu et al., 2002; Gur-Reznik et al., 2008 ). As a result, the total organic matter in rawrainwater was effectively removed through the FAD process.

3.4. Comparison of pollutants removal by FAD and conventionaladsorption

The performance of the FAD process in terms of the removal of

several pollutants has been discussed in the previous sections, andsummarized in Table 1 . To further illustrate the enhanced removal

of pollutants by the FAD process, a separate and conventional GACadsorption unit has been tested as a reference. The GAC unit hadthe same operating conditions as the FAD plant and it was placedin the same twin reactor, in which both the microltration andUV irradiation steps were removed.

The removal efciency of the GAC unit for all the tested pollu-

tants has been summarized and listed in Table 1 . As pointed outelsewhere, although good DOC removal was achieved by the sepa-rate GAC unit, the removal efciency of total organic matter andbacteria by FAD was much higher than that by only GAC. TheFAD process exhibited excellent capacity for organic matter re-moval thanks to the synergetic effect of GAC adsorption, microl-tration and UV irradiation. In the hybrid process, adsorption byGAC, three stages of biodegradation, separation by microltrationand oxidation by UV jointly contributed to the elimination of or-ganic matter in the raw rainwater.

4. Conclusions

The FAD process has been tested for drinking water treatment

from harvested rainwater. The following conclusions might bedrawn from the results of our study:

Pre-ltration exhibited a good total solid removal efciency inrespect to a moderate turbidity removal capacity and preservedFAD unit performance over a long time.

The FAD unit is able to produce pure water in terms of microbi-ological quality; it provides an absolute barrier for pathogensand several major contaminants, also reducing turbidity. Thecost of FAD units is relatively low, which makes the systemaccessible to small communities and households located indeveloping, water stressed countries.

More extensive studies are needed to understand the FAD ef-

ciency on other types of bacteria and chemical pollutants and toverify costs and applicability in developing countries.

Fig. 3. Removal of DOC (a), TOC (b), SCOD (c) and UV254 (d) by the FAD process.

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Acknowledgments

FAD treatment plant was designed and patented by ProcomS.R.L. (Firenze, Italy) and was provided for this research. Technicalassistance provided during the research activities by F. Santoriello,P. Napodano, S. Giuliani, D. Ricco and M. Landi is highlyappreciated

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